Oof, I'm sorry to inform you that this is normal. 1 million silver might seem like a lot now, but it really isn't once you get to mid to late game. 

i always excpect between 500k to 2 million per +16 upgrade ... that way im never bummed out :P

Just 1m :D Sometimes you lost over 2m silver. A 6 star accessories upgrade cost almost 50k and sometimes over 30 attempts need to success. If i remember good, the max attempts is 35 if use upgrade to 16 button, without instant upgrade.

It would be nice if it capped at 1 million TBH, as others have stated I've lost 2 million plenty of times.

I tend never to let myself go below 2.5 million in the bank as I don't like getting so low it impacts day-to-day tasks.  So in that sense try (unless I get weak) to only roll for LVL 16 with around 4 million in the bank

wait til its 2.5mil to do the last level upgrade ive had that happen plenty of times - its just one of those things that happens esp if artifact event on i find lol