The strongest argument for a small first deposit has nothing to do with market conditions. You are testing a process, from signup and verification to funding, a first position and eventually a withdrawal, and you want that test to cost as little as possible.
Run the whole loop starting at the ₱15,000 minimum. Deposit, wait, then withdraw part of it and watch how long the money takes to return and whether it comes back to the method you used. A platform that handles a small withdrawal cleanly is worth scaling into.
Only after that full round trip does it make sense to think about size, and even then in steps rather than one large move. A bigger deposit does not make a strategy work better, it only makes the same outcome larger in both directions.
Why the first deposit matters most
The first deposit sets the habit. An amount chosen because it is genuinely comfortable tends to lead to calm decisions; an amount chosen because it felt like the maximum possible tends to lead to decisions made under pressure.
A workable starting point
Money you would not need back within a year, in an amount whose loss would be annoying rather than damaging. That figure is personal and nobody else should set it for you.
Adding to it later
Topping up a balance you already understand is a far stronger position than starting large and learning the platform afterwards.
Questions worth asking before you send anything
How do withdrawals work, and to where? What gets deducted, and by whom? Who do you contact if a figure looks wrong? A platform that answers all three clearly, in writing, is behaving the way it should.
Investing involves risk, including the possible loss of some or all of the capital you invest. The value of investments can go down as well as up, and you may get back less than you originally put in. Do not invest money you cannot afford to lose.