Welcome to the forum. If you are in the US, I am rather surprised you did not find and consider the DA 18-135mm zoom lens, which is often bundled with the K-70 as a kit at a good savings. The 35mm and 50mm lenses you have are good lenses, however. The advantage of the Pentax DA 15mm f/4 Limited is its incredibly small size, in addition to its excellent imaging quality. I carry my camera in a belt/shoulder-strap holster-type case, and the little 15mm LTD WA lens goes easily into the case's front accessory pocket! I just put a patch of bubble wrap in the front for extra protection.
As an alternative, when desiring more range and flexible framing, the very fine DA 12-24mm f/4 is an excellent lens- highly recommended.
The DA 21mm Limited is wide angle also, but far less so than the 15mm lens. This makes it an ideal compact single focal-length lens of a very versatile, multi-purpose angle of view for a walk-around lens. Being just a single focal length, there's much it cannot do, but it can cover many situations. Working with just one focal length, and being thus restricted, is good for learning how to make best use of that focal length, and what its properties are.
In the old days, a 35mm film SLR camera body often came bundled with a 50mm f/1.8 or so lens, being considered having a near-normal perspective (front-to-back relationship of near-to-far objects in scenes viewed from a not-close foreground). On your modern APS-C sensor-size DSLR, the equivalent would be a 35mm lens. But a slightly more wide-angle field of view (FOV) would be more versatile, being applicable to more scenarios, and more opportunities for photographic interest.
As to the "scene" modes, Pentax does list this as a feature for the model, but does not spend money advertising it, because it is a common feature found in most entry-level DSLR cameras of most any brand. It is a feature that has been around for numerous years, and many previous models. If you find this to be a useful feature, then great that it is serving your needs well!
Many of us have been into photography since long before this feature existed. Some, like myself, since before there was auto-anything. No auto focus, auto "P" "Av" "Tv" etc. etc. Just a meter to read in the viewfinder (VF) and set your own shutter speed and aperture manually. So you had to learn the best setting to get the results you want, when facing one type of scene or another, and the lighting present at the time. "M" was the only ballgame in town.
As Big Mack, UncleVanya, and others have said, look upon the "scene" modes as a convenience but also a learning tool, and keep in mind that the convenience of automation carries with it a degree of less than optimum reliability or accuracy. So use it as just one learning tool. I currently shoot with 3 camera bodies, 2 of which are pro-oriented models having no "scene" modes, but one is the preceding model of the K-70, the K-S2, which has a very similar design, including the "scene" modes, which I never bother with. This is because I already know in advance what settings I will use in each of those "scenes", and often quicker and better than the automation.
There's nothing wrong with using this convenience, but one reason for owning a camera so capable as the K-70 instead of a point-and-shoot cam, is the ability of the photographer to take control. Avoid shooting with your mode dial set to the auto "green" mode. And reserve use of the "scene" modes for tricky specific "scenes" of extreme lighting situations. Instead, for fully automated exposure settings of aperture and shutter speed, use the "P" mode. It is just as automated, but will allow you access to controls to make adjustments on your own. In fact, one feature that is exclusively Pentax is the Pentax Hyper System. In the "P" mode, if the photographer, noting the info displayed in the VF or back LCD screen, decides on a different aperture or shutter speed than that the camera has chosen, can instantly change either on the fly simply by doing so using the thumb or finger e-dials to the extent that lighting will permit, instead of having to change the mode dial first to Av or to Tv. First click freezes current value, next click changes. A hit on the green button will restore full "P" operation.
In the "M" Manual mode, the green button can be used to instantly set a "correct" metered exposure of both shutter speed and aperture without having to twirl the thumb and finger e-dials until the meter indicates "correct" exposure settings. A real time saver. If wanting a different aperture or shutter speed, go from there. Both "Hyper Manual" and "Hyper Program" are exclusive Pentax features that could indeed be better presented by Pentax.
Also, go into the Custom Image menu ( having the mode dial on "P") and set "Fine Sharpening" in both the standard "Bright" and also the "Natural" categories. Then set the camera back to the "Bright" setting, which is best for most shooting needs. This will provide superior detail in your images.
You can access these and other menus quickly via the "info" button. Then the 4 buttons surrounding the "ok" button will serve for navigation, adjustments and settings.
Last edited by mikesbike; 08-06-2018 at 10:56 AM.