All sorts of things to consider, especially if the new or old role is bonus eligible and how easily you believe you can land a new role. 15% bump in pay for 3-6 months typically isn't worth much.
Let's say that you end up staying until June and get a new job in July and both positions are bonus eligible at 10% and you make $100k (to keep the math easy).
Your salary increase will net you $7500 in extra income in your first 6 months. You receive NO bonus for the first 6 months. In your new job you get $5K in bonus for the back half of the year plus another $7500 in pay increase. Total comp would go to $120k.
If you leave now you get the same comp PLUS the comp for the bonus accrued for the entire year. That gets you to $125k. You also have control over your destiny.
The only scenario that I would consider staying is if I received a large cash bonus either now or at a specific date that was mutually agreeable and that the bonus would more than make up for any missing bonus I would have received in my new role. You are the one being inconvenienced. To give up an offer from another company you need to be compensated appropriately.