I think you are thinking too much, pick the one that you feel better, if weight is important, the regular 15 is the best option; this year the Pro is lighter and smaller, so the gap is smaller. The plus is bigger than the PMAX, so maybe you can forget about the big ones.
Nobody knows what can happen next year, this year they put the regular 15 at the level of the last year pro, so... who knows!
Im tempted to get the regular 15, but I have the 14Pro and it feels like buying the same phone without Promotion and the extra lens right?