I plan to trade with XM by depositing $1500. Is...

Vincent Howlett: I've used the XM broker for more than a year and now XM is one of the brokers that I still use to compare price data. During my time with XM, I didn't find the spread widening or the profit and SL were cut before it reach the level. If that happens, I would move to another broker.
I suggest you test XM by trading on a real account with small capital. It usually takes 1-2 weeks to observe their spread. Pay attention to spreads when prices are normal, when near TP and SL, and when there is big news release. You can take notes or screenshots them as evidence. 

Wayne Finnie: 

I'm currently testing the MT4 XM demo and I can feel the movement of the price is solid, even I feel comfortable. But what I want to ask is, will the MT4 demo later be different from the real MT4?
Even though I'm profitable, I still don't feel like I can enjoy the results. In the long run, brokers don't seem honest anymore. I've traded with 3 brokers, some of them have blocked orders.

My other question is, can I trade for a living?

Vincent Howlett: 

My experience using real and demo XM is no different. I personally can't say for sure whether XM will not cheat but my experience can be used as testimony that this broker is fair.

I've also experienced the same as you, from widening spread, manipulating SL and TP, and so on. I personally have tested more than 10 brokers for this, and it was proven that some brokers are scams so I never used them again. Even some brokers are too "rude" in dealing with it, such as too long requotes, or positions that cannot be opened at the time of profit.
There is a small number of honest brokers who just pay their profitable clients and don't cheat. Your job is to find such broker.

Of course, you can trade for a living.
I want to tell a little story, from my experience meeting many traders from various regions, most of them (95%) cannot reach the trading for living level. The get-rich-quick mindset, trading without money management, and untested methods are the reason the trader can't last long in the market. In addition, it is very rare to find a trader who is disciplined and consistent with the trades they made. Back to the broker for trading for a living, I recommend choosing a broker that is regulated by an international regulatory body, namely: CFTC, NFA, FCA, FSA, FINMA, MiFID, ASIC and FMA. They have better and safer regulations than brokers from offshore countries (offshore) such as seychelles, cyprus, british virgin, island, belize, vanatu, etc. The drawback is that regulated brokers usually have a fairly large minimum deposit.

Wayne Finnie: What I don't like is how sneaky brokers are. When I chat with CS, they just ask me to follow the policy on client agreement, but then when I read, it's already newly updated. Things like this make me scared to deposit in huge amounts.

Vincent Howlett: 

Open real accounts with CFTC, NFA, FCA, FSA, FINMA, MiFID, ASIC and FMA regulated brokers.

The brokers below are good because they have strict regulations and have a long history of forex trading.

IG (min deposit $300), Forex.com (min deposit $1,000), Oanda (no minimum deposit), Saxobank (min deposit $5,000), XTB (min deposit $250), Dukascopy (min deposit $1,000)

Those brokers are different from offshore regulations such as Cyprus, British Virgin Island, Vanuatu, Grendlines, Belize, etc. You can also check the detail of each broker above, including regulatory aspects, company history, to liquidity providers.