At one time Deist was the only manufacuturer of -20 gloves so -15's I believe are allowed with -20 suits. If you have never driven with -20's it's like using boxing gloves. Same with -20 boots.
I belive Deist, DJ, Simpson, Impact, Leaf, and Stroud can make what is required. Look up Top Fuel/ FunnyCar suits if you are going used. I have bought both my -15 and -20 as display models at a significant savings so look to what Joe has.
I would advise anyone to have a suit prior to putting a roll cage making sure you can fit in your car and reach everything easily. Make switches far enough apart for your gloves to operate. Fit yourself many times in your car with everything on, helmet and padding too. Have your belts and restraints set for the driver before inspection. I would also advise anyone new to sit in their car for 30 minutes in the hot sun....Then you would be prepared....................Good Luck.