Haven't been on a bike in 15 years. Been on 5 minute ride up a hill and throat is burning. 15 minutes late still wheezing, is that just because I'm so unfit and will get less the more I do it

Also when I was in gear going up hill inside of smooth pedalling it was like I'd peddle a rotation and then have to start again it wasn't a smooth ride hard to get any rhytmn going when you have to do that. Would that be the poor quality of bike?

Thanks