Both line-ups bring a range of cosmetic, mechanical and spec improvements designed to boost the appeal of Audi's fastbacked sedan as it enters middle age.
Like the A6, the A7 range has also been rationalised.
The S7 continues to offer big performance from its twin-turbo 4.0 litre petrol V8, though minor upgrades help eke out slightly more power and economy.
More importantly, the price of entry has dropped by a massive $21,350 for the A7 3.0 TDI.
The A7 3.0 TDI Biturbo enjoys a more modest price reduction of $4700, but an increase in standard specification brings an added $6464 in extra value.
The S7, meanwhile, undergoes no price movements, but gets a value boost of $5943 thanks to added equipment.
As with the A6, the A7's base 3.0 TDI engine is less powerful than last year's model, boasting just 160kW rather than 180kW.
Torque has also been reduced from 580Nm to 500Nm, but the tradeoff is an improvement in fuel economy from the MY14's 5.9 l/100km average, to the MY15's 5.2 l/100km.
Meanwhile the A7 3.0 TDI Biturbo gets a 5kW power hike to 235kW (torque stays at 650Nm) with fuel economy on the combined cycle moving to 6.1 l/100km.
The S7 flagship (until the RS 7 arrives), makes 331kW and 550Nm from its 4.0 litre V8 - 22kW than last year's S7.
Despite the extra power, fuel use falls to 9.3 l/100km, a reduction of 0.3 l/100km.
All A7 and S7s take power to all four wheels via Audi's quattro AWD system, with the S7 also getting an active centre differential that can vary the front-rear torque split according to conditions.
Both the A7 3.0 TDI and S7 make use of a twin-clutch seven-speed automatic, while the high torque output of the 3.0 TDI Biturbo sees it use a more rugged eight-speed conventional automatic.
The S7 rides on adaptive air suspension, unlike the conventionally-sprung diesel variants.
While the interior is broadly similar to last year's A7, the MY15 A7 and S7 receive a substantial infotainment upgrade.
For starters, the space between the tachometer and speedometer is now taken up by a reconfigurable colour LCD display, that can display everything from the song currently playing, trip computer information, your phonebook and the sat-nav map.
The infotainment system itself is the latest evolution of Audi's MMI Touch system, which incorporates a touchpad with a familiar scroll wheel and shortcut buttons.
For 2015 though, it's run by a more powerful processor that gives smoother, crisper graphics and faster response times.
A key change is the ditching of Audi's proprietary interface plug, which has been replaced by a pair of more conventional USB ports.
One USB port is also capable of putting out higher current, to charge the latest generation of smartphones and tablets faster.
Other standard features include LED headlamps, 19-inch alloys, leather upholstery, a 600W 14-speaker BOSE sound system, quad-zone climate control, front and rear parking cameras, parking sensors, a digital radio tuner, lane keep assist, blind spot monitoring and a powered tailgate.
Move up to the 3.0 TDI Biturbo or S7, and you get 20-inch alloys, active cruise control and a glass sunroof.
Options for the range include a self-parking feature, self-dimming Matrix LED headlamps, a head-up display, Bang & Olufsen premium stereo and the S Line Sport package.
PRICING (excludes on-road costs)
- Audi A7 3.0 TDI - $115,400
- Audi A7 3.0 TDI Biturbo - $144,900
- Audi S7 - $179,900