It isn't possible to OSRS gold transform money into more. You must do herby run to develop profitable skills, such as the hunter, the fletch yew longs, anything similar. Someone said 99 fishing, I'd say that's probably it but make sure to catch rocktail fishing between 90-99. Hell yes you can but it's a slow and a long road, dependent on the point at which you begin and how committed you can transform 1gp into 1B in a matter of minutes.

The way I'd do it , even though you've now got 15M is to buy something which bounces up and down in value, but gets caught at the bottom because of its alch price; at this point , you don't need to take big risks with your money but slowly building it up and 15 million which is a decent amount can bring you around 400k per period of the green chaps as an example.

Since they aren't able to drop below 2200 for a long time because they have an average alch of 2380, you could buy them for 2200-225 and sell them for 2300-2350. It is not the fastest method , but it's consistently successful, in the event that you're a member you are able to purchase more exotic items like black chaps for 5400 and selling for 6000+ , however if you do not plan it correctly, it could mean you hold stock for a while.

Do not buy red dragonhide, as it's not very popular and you should stay clear of seeds as they're the scourge. I've lost an absolute fortune dealing with them. The way to do this is to access the graph that shows the 180-day period and see what bounces constantly between two points and purchase and sell before they hit them.

It requires some practice but after a while it's possible to make amazing profits of about 1-2 million everyday...do some slayer or woodcutting while buy RS gold you are at it so you don't waste time either.