Ok.You've asked why the price of bitcoin is so high.Actually there is a significant reason of it.You may be know that there are a fixed number of bitcoin in this whole world.But the number of buyers of bitcoin is increasing day by day.So,to cope up the number of supply and demand,the price of bitcoin is so high.
Bitcoin is a digital currency ,now it was accepted by Amazon also and investor of bitcoin also now a days increased so if buyer increased one product the rate also increased simultaneously.But I think 15k$ is not high value as compared to last week of 20k$,so you can inverse now to get some profit.