Is there a point in recalibration of scores for variant calling?
I personally don't think BQSR has a huge impact on variant calling, but you don't really need to guess. If you run GATK BQSR, it outputs a table and charts of exactly how much quality scores are adjusted. The adjustment will vary depending on the position in the read and genomic context (previous and following base). In my experience, the difference is a few points at most, but it's certainly noticeable.

GATK recommends BQSR for both genome and exome data, which is normally much higher than 15x.