There's so many sensors these days it really take a high- end scan tool and a competent technician to interpret the codes down to the actual problem. My first thought would be a bad O2 sensor throwing off that code. 2nd would be a vacuum leak. Here's a decent (short) read which might give you another clue or two. Good luck. https://www.700r4transmissionhq.com/p0175-ford-f150/

 

A vacuum leak would cause a lean code(undetected air entering). And I doubt a bad o2 caused that code

 

Lean/rich codes are tricky and most times hard to understand, most people myself included at first, thought a rich code meant there was an excessive amount of fuel being detected in the exhaust stream. It's not a fuel sensor it's an oxygen sensor It doesn't care how much unburned fuel is there, it's seeing an excessive amount of unburned oxygen in the exhaust stream.

Only way to diag it is by running a battery of tests on the system.
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I recently purchased a 2010 F150 5.4 V8, with 150,000 miles. I am seeing a similar issue only when starting a cold engine and the temperature is also cold. The starter will crank an excessive amount of time (about 10 seconds) before finally starting. The worst occurrence was last Friday when it wouldn't start at all. I had it towed to a shop and the error code was a rich mixture. After getting the truck started, and keeping it over the weekend, they weren't able to reproduce the starting issue. The kept the truck in their garage. I made a couple videos of the starting issues I have seen to show the technician. Last night the engine was cold after sitting 8 hours and the temperature was about 30. When I turned the key it was a repeat of the same 10 seconds of crank time. After sitting overnight and starting this morning, there was a little extra crank time maybe 4-5 seconds, but the temperature was about 34 this morning. Once the engine is warm, starting is essentially instantaneous as expected.

When picking the truck up from the dealer, the dealer had put about a half tank of gas in the tank, and I stopped to fill the tank on the way home. As the engine was warm, there were no starting issues. The technician and I have discussed everything from a bad fuse, fuel pump going out, E85 fuel to bad gas. It still has just over half a tank from the initial filling.

I dropped the truck off tonight and the technician will start the truck cold in the morning. Hopefully, he will be able to reproduce the issue and solve the problem. I will share this thread with him which may help. I would appreciate any insight the group may have of this issue.