nice...I run the 1520 on 5s and love it in my mbx5t
1. MBX-6 T8 1900KV, RX8 ON 4S
2. MBX-5T 1520, MMM ON 5S
3. MBX-5 ONROAD CONVERSION 1515, MMM ON 5S
4. MRX-3 ON ROAD CONVERSION 1512, MMM ON 6S
5. TEN T 2650 T8, MMP ON 3S
Very little, you should go for 5 or 6S with the 1520 to see a big difference.
Maybe a 1518 1800kV and 4S ? but same you should run it on 5S.
6S 1520 geared for 40mph will give best results I think.
Inferno VE MMv3 NEU-CC 1515/1Y 4S "Flying machine"