The only real way to get to level 15 Woodcutting is to do normal logs. I usually start in Lumbridge Forest.
Now move onto Oak Logs. There are a few places where you can head. Draynor Bank is a really good option.
Level 30-99 (Free To Play)
Willows are the best from these levels. You can either Powerchop or bank them.
30-99 (Pay to Play)
Hit up Willow Trees till 60-65. The best spot is Catherby, just west of the bank.
From 60-65+ (Pay To Play)
You have two options. Continue cutting willow logs until 99, or you can move onto Yew Logs at around 75. This is totally up to you. Willow logs you won't make much of a profit at all, but Yew logs you will get at least 10M Gp.
I hope this guide has helped you beginners at becoming closer to your 99 Woodcutting.