The 1930 should do OK in a buggy. I have seen (here on RCM) other truck setups running the 1930. They ran a bit hot, but were in trucks. I've never had a Lehner, so I can't say whether the 1930 is comparable to a 1512. The 1512 is kind of short, but has a rather large diameter.

Since you already have the 1930, I'd see what it'll do. I would go ahead and reconfigure it for 1500kv, as I think that 2600 is too much. I think you'd be better off gearing up rather than trying to gear down in a 1/8 scale application.

I just started running a Neu 1512 that was supposed to be a 1900kv motor, but I suspect that I got a 1400kv motor by mistake. The more I gear it, the better it gets. It isn't super fast, by any means, in my truck on 4S; but it is fast enough for a track and I can run more cells through it. On 5S things start to get nuts. Lots of power on the 5S and 6S is still possible. If I keep the motor, I'll get a couple of 3S packs to see what it will do.

Since I started all of the brushless stuff, I've found myself going to lower and lower kv motors. Speed is nice, but when the excitement of speed wears off and you gain more of an appreciation for cool dependable running, the appeal of the lower kv motors really starts to show.