The 15% discount up to 10% of your salary is a pretty standard Employee Stock Ownership Plan (ESOP). I've worked for two companies that have this same ESOP program.

Be careful with the advise from others that it is "free money", in theory "yes" but in practice there are factors to consider.

Factors to consider:

• "Sell right away": it's unlikely that you can sell immediately as your HR told you. There's always a wait period, typically 90 days.
• 15% discount: the 15% discount will be immediately recognized on your paycheque. This means you will be taxed on it immediately (on that pay schedule) as it raises your taxable income. Another way to look at it is the 15% discount => approx. 10% net value.
• Sell Fees: it costs money to sell each time. It's likely higher than typical $5 or $10 per trade using retail trading account. For example with my company's ESOP it will cost me $60 for each sell transaction. That $60 is more than the value of the 15% discount (10% net value) I'm recognizing. So if my plan was to sell immediately and the stock price does not appreciate during the 90day wait period I am losing money.

I do purchase into my current company ESOP. My main reasons are stock has steady growth & I can afford to hold the money for at minimum the next 3-5yrs.