If currently there are 15 swans in the pond, in two years' time there will be 15*2=<<15*2=30>>30 swans.
In another two years, the number of swans in the pond will double to 2*30=<<2*30=60>>60 swans
In another two years, the number of swans in the pond will double to 2*60=<<2*60=120>>120 swans
If after 6 years there are 120 swans in the pond, in eight years times there will be 2*120=240 swans
In another two years, which is 10 years, there will be 2*240=<<2*240=480>>480 swans in the pond
#### 480