Amperage in a voltage divider is absolutely relevant, especially in a battery powered situation. While your setup is a large scooter battery, and this is more relevant to small battery powered design, a resistor voltage divider is still a load, of R1+R2, to ground. Too large a resistor value, and you are wasting power through the resistor pair. At 7.5Ω + 7.5Ω, a 15Ω load, you would be wasting 1 AMP of power. At 1k + 1k, a 2k load, you are wasting 7.5 mA. A 2k + 1k pair is 3k load, 5mA wasted.
Additionally, the larger values will need a larger Wattage rating. At 1k + 1k and 15V, you are wasting 7.5mA * 15v = 0.1125 Watts. Since this is through two resistors of equal value, they share the power wasted, 0.1125 / 2 = 0.0565 Watts. A typical 1/8 (0.125) Watt resistor will work. At 375Ω + 375Ω, or 20mA load, each resistor will waste 7v * 20mA = 0.140W, so a 1/4 Watt resistor would be needed. Too low wattage a resistor can burn out. Too large a resistor can waste too much power and catch on fire or burn you.
You should choose a higher pair with the same ratio (2/1). A 24k R2 and 47k R1 will work the same, while providing only a 0.2mA load (210 microAmps). The Ratio stays the same (1/3 of Battery Voltage).
But no, the amperage is not relevant to the Arduino's Analog input, or the Arduino itself. Unless you connect something wrong of course. The only concern is making the voltage divider too small (can't be read correctly) or too big (drains battery quicker).