The min supply voltage of the STP16DP05 is 3.0V, so No chance of reducing it any further while adhering to the limits.
It looks like the only options are either 2...3 of your IR LEDs in series, or using simple rectifier diodes in series with your IR LEDs. Depending on the switching frequency, zener diodes probably cannot be used due to their higher junction capacitance. However - that only moves the heat from the driver to the additional pn junctions.
Good luck!
/Peter
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