The way I would do it even though you've 15 million is to invest in something that fluctuates in price, but is held at the bottom by its alch value; at this point, you do not want to be taking big risks when you invest your money however, building it slowly. 15 million which is a decent amount will gain you about 400k in profit per cycle of green chaps, for instance.

Since they aren't able to drop to below 2200 in a very long time since they have an average alch of 2380,, you could buy them for 2200-2250, and sell them for 2300-2350. It's not necessarily the most effective method out there but it's consistent. if you are a member you are able to purchase higher priced items, like black chaps, buying at 5400 and selling at 6000+ , but if don't plan it correctly, it could mean you hold stocks for quite a while.

Avoid red dragonhidesince it's not very popular and also avoid seeds like they're a plague. I've lost a fortune in them. The way to do this is to access the graph over 180 days and examine the bounces constantly between two points and purchase and sell before they meet, it requires some time and practice, but once you get it right, you can make enormous profits of 1-2 million everyday... do some slayer or woodcutting simultaneously so you're not wasting time.

Herb running (in definition) is the running that runs between all of the herb patches, usually in the most time efficent method. It takes time to perfect an effective route that runs among the ones in the undulating water (forget its name) that is near draynor manor, the one north of ardyand the one in Catherby, and (if the quest is done) the patch up in Trollheim.

The goal should be to grow (usually) the most profitable seeds of herb which yields the highest profit when it's harvested. I'm not sure of what is the ideal starting point or even on the current pricing. However, I'd probably not suggest you doing it with the current level until after you unlock additional herb options.

Doing Fairytale Part 1 is a major benefit in that the secateurs increase the amount of herb taken. Another suggestion if you're planning to do some herb runs in the future is to invest in the Herb Scroll of Dungeoneering as it will offer a possible "money back" should you be lucky. Also, doing Ghosts Ahoy! will aid you by providing the ectophile needed for an easy teleport to the swamp patch. If you complete the lumbridge/draynor steps, it can help you get an easy teleportation to the draynor patch.

If you are farming, it is recommended to also use supercompost EVERY TIME. Particularly when you're trying to make profit from your herb growing. Also, to remove any doubts, you are not able to make a payment to a farmer who will watch cheap OSRS GP your herb gardens, you can only pay him to monitor the vegetable plots and the fruit at the allotment.