While dividends are cash flow rather than income, it's somewhat different with preferred stocks since they are a hybrid security, leaning more toward fixed income.
The bulk of them are issued at $25 and are callable in 5 years at the discretion of the issuer with a maturity date which can be decades or even never (perpetual).
There are three primary risks.
The first is the quality of the issuer which is fairly easy to achieve. Only buy investment grade issues. Don't buy junk (C or lower).
The second is longer term interest rates. Preferred stocks behave like bonds and move inversely to rates. They may over react to Fed fund rate increases but they tend to recover from that in a reasonable amount of time. A perfect example of this occurred in the latter half of 2018 when preferred stocks were whacked as rates rose. They've risen more than 10% since then even though rates only dropped modestly. This behavior would be irrelevant since you indicated that you don't care about share price value.
Lastly, most preferred are callable in 5 years. When called, if rates are lower, you won't be able to replace your higher income positions and your yield will drop. Warning: Don't buy preferreds that are significantly above par and are callable in a year or two.
To answer your question more specifically, investment grade U.S. preferred stocks currently pay about 5.6%. To generate $1,500 a month, you'd need about $321k, even more if you have to pay taxes on the dividends and you want $1,500 per month after taxes.
And while trading appears to be the bane of this board, you can bump that 5.6% yield up several percent by occasionally swapping out appreciated issues. Even more than that when there's an interest rate cycle, something we haven't seen for more than a decade.