It's an important consideration to think through.
Buy bitcoin now. Don't wait for scaling solution to end because the price of bitcoin will definitely grow after successful upgrade.
You can compare it to Litecoin - After SegWit signalling ended price of LTC skyrocketed, it will be the same with Bitcoin.
I don't think Slark fully grasps all of the consequences that could come from the fork. It's not about whether bitcoin will go up or down, it's about where you keep your bitcoin and whether you'll be shut out (or not) from the alternative bitcoin version that could be created as a result.
Segwit could still result in two bitcoins.
A safer alternative to exposing yourself now would be to spend your investment on Ethereum or Litecoin. Both have been relatively more stable than Bitcoin and Litecoin could even see another pop up to the $100 mark this summer.
Well, I don't think investing in other coins was part of the Q., but maybe it was. I would say, start buying now, split the 15,000 into 2. Buy half before August 1 and buy the rest after Aug first. Buy slowly before and buy slowly afterward. When the price drops, you will get more for your money. When BTC forks, you will have 2 different bitcoin piles. So if you have 100 Bitcoin before the split, you will have 200 after the split. No need to worry about it. Both piles are safe. You will be able to sell both afterward, but you will need to do a little reading on that subject.
Ethereum is an 80% pre-mined coin and is also a centralized benevolent coin.
Litecoin would also be a good choice I think, if you want to spread your money around a little.