Originally Posted by
ALadyNCal
Appreciate advice for our routing -- REALLY don't want to collect/lug/re-check bags
IST-FCO-LHR (AZ)
12 hours overnight LHR hotel
LHR-LAX (VS)
My hope is that we can check large bags through to LAX when departing from IST airport. Is that likely? REALLY wanted simple (no luggage!) departure from LHR

Thanks.
As stated above, if you have an overnight layover then VS, nor any other airline at LHR, will not hold your bags for you. You will have to collect them and recheck them when you check-in for your LAX flight.
Secondly, are you on one booking for all legs? If not then you likely won't be able to check them through anyway.
BTW this rule is not VS's one, it's an airport / security requirement. However if you do check bags through and have a long connection time then simply avoid 'Flight Connections' and exit through normal immigration and customs. If you go through flight connections you re-enter the secure area of the terminals and then, I don't think it is possible to exit again nowadays ... more infernal security!