Yes, the R is a speed rating of 106 mph and the T is 118 mph. So you can use the T rated tire if you wish.
135 - T20, T15, D15
I believe you are referring to either a t5 or a t150 transmission. So the answer is no, a t15 will not fit.
61 - T15, D8
65 - T15, D10
155 - T20, T15, DB
145 - T20, T15, D20
141 - T20, T15, D18
121 - T20, T15, D8
You go to the local hardware store and pick up a torx bit driver for a t15. It looks like a screwdriver with a starbit head instead of a flathead or phillips.
torx heads. I cant remember the size. might be T15
It should be a number T15 or T20.
Torx T55