Hi @marthaann ,
There is a lot of discussion online regarding latency (delay) problems when using BT between devices. On some devices this is more noticeable than on others. Without seeing the video at the same time you'd probably not even be aware of it,
There will always be a slight delay as you have to convert the audio signals from electrical to wireless and back again to electrical. To prove this try connecting to the speaker via a cable using the aux input, (thereby keeping the audio an all electrical signal). You'll find that the latency is significantly reduced.
The length of the delay time seems to vary between makes and even models If you can try using a different BT speaker to see if it is any better or perhaps even worse
You could always try and see if there is a firmware update for your speaker (you don't state the model ) by using the JBL Connect app (available at the Apple app store) which might improve things. Then again it may not.