[2019] Advice on Monitor Size

You've already received a lot of good advice and a monitor is a pretty significant investment unless you are a hobbyist who spends a lot on having current gen technology.

I personally like having a second monitor and have found I can't really live without it. Netflix, Twitch, looking something up....it's invaluable to me. As a result my main monitor is only 27" or it won't fit well side by side with my 19".

The other consideration you may look at is 60hz vs 144hz. If you aren't planning to use a card that supports 4k, I highly recommend 144hz as it won't change your world but the visual difference is slightly better and it's a nominal additional cost to a 1440p monitor anyway.

Regardless if you are on a 15inch laptop you'll see a vast difference in your gameplay. Congratz on your upgrade!