Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
Very little chance of through-checking on separate tickets. Don't forget that you will need an e-visa to go landside.
Are you planning to overnight in the lounge?
I'm sure someone with more recent IST experience will come along, but I'm not sure that you can drop off your bags the night before a flight.