How can I keep fix choppy and slow performance on Premiere Pro?

I am a newbie, but I have watched many videos on this topic and nothing seems to help.  The problem is that playback has all sorts of hiccups, like stills not appearing in playback or animated clips appearing as stills or the screen simply showing black as only the audio plays.

The problem may be that I started my first project as 1920 x 1080, but I see no way to change that without starting my project over again, which I'm hoping to avoid.   I see plenty of videos about changing the size of sequences, but none for changing the size of an entire project.  Despite that large size, my video contains only audio and still images with effects, no heavy-duty video footage, yet things only run smoothly in fits and starts.

Here's what I've tried:

Rendering sequences:  This turns the timeline green temporarily, but on playback, little red patches appear, making the playback "hiccup" visually speaking at the start of each new clip.

I've set the playback resolution to 1/2 (all smaller resolutions are greyed out).

I've tried to work with proxies, but I'm not sure I can do that with a project that contains only audio and stills with Adobe effects.  Media Encoder can't make proxies for jpegs and pngs as far as I know. At any rate, when I right click on clips in the bin, the Proxy option either doesn't appear at all, or the interface appears with all options but "cancel" greyed out.

My computer model is Dell G15 5510 with an i7 processor, which I bought recently and which the sales guy told me was top of the line for image processing -- tho' I guess that's just when it comes to laptops.

Most of the folks who create videos on this problem seem to imply that I have an old or slow PC, which bothers me a tad since I paid top-dollar for what I was told was the best laptop for videos.   Yet I'm guessing now that laptops aren't the right kind of computer for working with Premiere Pro.

Should I start over at 1080 or 720 in order to achieve reliable playback?  Or is there something I'm missing that would help me avoid these sorts of problems without starting a new project at a smaller size than 1920x1080?

Thanks!