I'm sure a few others will chime in, but pretty sure that OEM is a bando. If you open it up and take a look there might still be some printing on the old belt, assuming it's the original anyway.
https://www.partsforscooters.com/106-121-Bando-Belt-781-20-30-Kevlar for instance.
There are probably some aftermarket ones that'll work too. Stick with the big names and you'll most likely be fine.
Some peeps may flame me on that, but I ran a Malossi or a Dunlop on about half a cannonball on my S200 then added another thousand to it before selling it. It was still fine.
The Bando's still cheap enough these days though.
Probably a good idea to check the rollers and the affiliated little sliders (not to be confused with the sliders you can use instead of rollers) on the ramp plate.
I'd just change 'em out personally. Maybe drop a gram on your rollers, possibly try DP sliders vs. rollers.
The DP sliders I installed on my S helped a bit, definitely with an acceleration dead spot it had, but I really should have dropped a gram as well.
I did that on my SYM and it cut my mpg a tad but well worth it. I have 1 gram lighter rollers on my other SYM. It grabs quicker than the sliders and has a bit more acceleration, but is not as smooth.
This thread talks about that a bit regarding the People 150 specifically. Looking like 18X14 - 15g is stock per one post
https://www.kymcoforum.com/index.php?topic=1966.0and per this handy chart
https://www.scooterworks.com/blog/2012/11/13/roller-size-chart/How many miles on the bike?
