VW Golf 2015 MK7 slow heater

What is your question?

Golf TSI 2015 Mk7 Hi, looking to fix a slow heater - I get slightly warm air but coming out the vents but it can take a long while before hot air comes out in -10F weather (up to 30mins+ when it's really cold). Engine temperature rises normally to halfway and coolant level is normal (never been flushed - less than than 40,000 miles). I have standard heating system (not the clima-control). I'm suspecting a sensor. Any good tips to check out first?

What makes this problem better or worse?

cold weather

How long has your 2015 Volkswagen Golf had this problem?

3 years