Double spending the transaction from the senders end is the only way out now just like you have started but the problem now is, he can only do that if he is not sending from an exchange or any of the wallet that is cannot be imported into electrum
I tend to agree if the wallet sender supports RBF that would be a great option to boost the transaction using double spending but if on exchange there's nothing he can do but wait until it is confirmed. It's two weeks have passed and eventually, if the transaction does not push through in 14 days, it will drop from the mempool and back to the sender's wallet. I think OP needs a few more days before that will happen since it was already 14 days have passed.
We should always check the mempool space for the transaction fee if you're in a hurry and don't use below 10 sat/vB fee for transactions because it will eventually stuck and you need to wait a couple of days.