I think you are over-diversified. It's unlikely that one will find 15 really great coins. Even more unlikely that the best timing for buying these coins would be during the same month.
You could have bought and held eth or neo for 3 months and just lost money if you had bad timing, same with any coin. Long term - product quality. Medium term - Market state. Short term - Coin price state.

It doesn't matter if you buy a great coin if you only hold for 2-3 months and either bought when the market was ATH or bought when just that coin hit ATH.

Personally I hold 5 alts + btc. Each of them is according to me the best coin for that time period.

1 very long term (3 years)
3 medium term (6 months)
1 short term (1-2 month)

If you find a good looking coin, follow if for 2 weeks and to learn it and wait a good op to buy it. Perhaps do nothing but sell off some coins and convert to fiat to buy it in the next market dip.
Never rush-buy any coin. Its better to miss out on several coins than to sit with a big bag of ATH buys.

If you do good research on every coin, price fluctuations won't  affect you as much. Just trust your analysis.
I have had very good gains in my investments and I have never bought ICO. I buy it 3 months after ICO when I can see some results and not only ICO hype and talk. If something goes up 3000% from ICO I only get maybe 1500% but I never lose money.