The ground rent should definitely be bought out on this one.
Technically it should be difficult to sell this house as there is under 70 yrs to run on the lease.
Also if you do nothing until there is less than 15 yrs left to run on the lease it will cost more to buy out.
Right now it will cost, as purchase price , approx 20 x annual ground rent. There will be ancillary costs but definitely this needs to be bought out before 2019