Thanks zozozo and mamya. I'm happy to know about a new amphibian and that the bridge opponents could be side by side in 23d. But I still don't get 15a.
Ethereal, I was stuck on 15ac at first because my knowledge of Indian geography is poor. However, the definition is end, as in objective, the first bit is in India and if you have 7dn, you already have the left bit.
Are the first 3 letters of 15a an acronym for an Indian border feature? And I can't find the connection between the letter I and Left though there must be one. Izquierda? Indent? Just 2 letters away from my curiosity's satisfaction...