How to know whether fuse is sufficient for electrical device?
1500 W/ 230 V = 6.5 A

800 W / 230 V = 3.5 A

Now, a fused circuit should normally be loaded to 80% capacity.  So on a dedicated circuit, you would need an 8 A or 4.5 A fuse.

But, usually circuits feed more than one outlet.  So you need to find out what else is being fed by the same fuse.  Most devices will have a sticker declaring the draw.  Add up the amps, add in your pump, and stay withing the 80% capacity limit.  If you go over, add another breaker/fuse and make it a dedicated circuit.  If amps aren't posted,   W/230 will give you the current draw.