Will 15 x8 Wheels with a 5x5.5 bolt pattern fit a Ford '83 F-100 ok?

Wheel / tire size changing is new to me and I can't seem to find appropriate help/answers elsewhere online at this point. My father passed away & left me his '83 Ford F-100 XLT pickup truck and although it's in very good condition… He somehow, for some weird reason, put 20" wheels & tires on the truck when it's suppose to have 15" wheels. I have done enough research to find that the original wheel size is suppose to be 15"x(?) + 5x5.5 bolt pattern. I have not been able to find offset & all that other mechanic techno-garble info. And the original tire size is suppose to be P195 /75r15sl. I have tried going to tire shops and every single one has said that yes those 20"s are not good for my truck (which I already knew that just by driving it) and that I should still up-size from the original since those p195's are like tiny car wheels. Every mechanic has recommended P235 /75r15 and that that size shouldn't affect the engine and transmission performance very much (if at all). Just to adjust for a slightly off speedometer of up 5 mph. 60 reading = 65 actual speed. Ok… I can live with all that if that is actually true. My problem is… Finding the proper wheel measurements because so many sites will say that the 15"x8" with 5x5.5 bolt pattern won't fit my truck of the wheel listed below but suggest other wheels of the same damn measurements. Will the wheels below fit & be safe to have on my truck with the P235 tires?

https://www.summitracing.com/parts/twg-71-5885/overview/

The OEM wheel and tire size of your Ford F-100 was 15x9 wheels with a -19mm offset and a 5-139 bolt pattern. 32X11.5-15 sized tires would be the most applicable with stock sized rims.

If the truck hasn't been re-painted or suchlike - that info should be on a label on the driver's doorjamb. Also, I would not run a P (stands for passenger) on a truck. Use LT (light truck) instead. The measurements g used are in inches, not the metric you learned. 32 = inches in diameter, 11.5 = tread width in inches and 15 is wheel diameter in inches.

I run M+S rated 31x10.5x15 on my '95 F-150. My speedo reads correctly.
The recommended size had my speedo reading high - not really going as fast as it said.

Jaka