I think if you have been growing 15 years already, then looking into some different strains would be a good idea. Many different strains are suited to different styles of grows and growers, and some strains just don't yield much for anyone. There is a hundred little things that could help yield, but with you being an experienced grower, above all I think some new genes would help you achieve a bigger yield. Also remember that Indicas are not the only way to huge yield , some Sativas and hybrids out yield most of the popular Indicas of today. Anyway good look!