if your primary reason is for commute and you want something with more poke, those clutch 150cc kapcai are quite nice.

1) the cost of ownership is not going to be all that much, you spend more on tyres but that's about it.
2) the "service" you mention kind of look like lube chains? so u mean to say that you don't even lube your own chain? actually you are best served if you learn some basic maintenance and lubing chain is the most basic or all basics that all bike riders should learn. i don't know where you stay so I can't advise you, but these 150-ish cc Yamaha are not exotics so any mechanic who is not utterly incompetent should be able to keep it in good condition.
3) in terms of power they are really no difference from a higher end kapcai and you gain more technology aid over the kapcai. the only difference would be riding position and slightly heavier weight. also if you are looking for those with clip-ons you lose some steering angle too. other than that its really very easy to get used to. u be riding competently in no time at all.

The R15 will be a bigger difference compared to the kapcai than the MT15 mostly due to riding position. i might have mentioned that the R15 is aggressive but that is me referring to a completely new rider. its kinda like getting into a road bicycle as a first bike without even riding a BMX before. but in your case you have ridden for almost 10 years so the R15 would probably not feel that aggressive. but no point talking about it, just swing a leg over the bike at the shop and see what you feel about it.

if you like the looks of the MT15 then it is probably going to be a better bike for commuting. but to me it is way too hideous to consider. for me its a case of "if you gotta be that ugly you better be fast"