How much does Genetics play into how long it takes to get pregnant?

Britney • I'm a happily married to the love of my life and I'm a 27 year old who is graduating university soon this year and is hoping to start having some beautiful babies soon! We have had one pregnancy and miscarriage at 7 weeks so far hoping for a rainbow baby
Does anyone know? For my mom and dad it literally took one try each pregnancy to become pregnant lol so my family is very fertile but my partners family it took his parents four years to conceive what do you guys think? Or is it just lucky chance?