Mash pH

I assume you meant teaspoon? ~15g of each in a 5 gallon batch seems high to me (and my own water is pretty bereft of those minerals).

Personally, I’ve never even tried it since the local water here is already bordering on too much sodium (our water is practically mineral free except for sodium. carbonates, and the chloramine added for sanitation).  I just treat for chloramines with campden, adjust acidity (or in our case lack thereof, i.e pH of 8.5), and add CaCl and CaSO4 to suit the style I’m brewing.

A tablespoon of each wouldn’t kill any brew starting with soft water and would certainly fix the pH issue.  If your water already has some minerals then use less.